Electronic ballast with controlled DC supply voltage

Abstract

In an electronic ballast, a half-bridge inverter is powered from a DC voltage and provides an AC output voltage having a waveform with trapezoidally shaped half-cycles. The DC voltage is obtained by way of a pre-converter with a control input operative to permit control of the magnitude of the DC voltage. The AC voltage is applied across the primary winding of a leakage transformer, whose loosely coupled secondary winding is connected across a gas discharge lamp. The internal inductive reactance of the secondary winding constitutes a lamp ballasting means by way of limiting the magnitude of the resulting lamp current to a desired level. Prior to the flow of lamp current, the magnitude of the DC voltage is controlled by negative feedback to the control input so as to remain at a maximum level. After lamp current has started to flow, by negative feedback derived from the lamp current itself, the magnitude of the DC voltage is reduced so as to bring the magnitude of the lamp current down to the desired level.

What is claimed is: 
     
       1. An arrangement comprising: a DC source operative to provide a DC supply voltage at a pair of DC output terminals; the source having a control input operative, on receipt of a control signal, to control the magnitude of the DC supply voltage; the DC source being characterized by causing the magnitude of the DC voltage to reach an undesirably high voltage level in the absence of the control signal; the DC source also being characterized by providing the control signal to the control input whenever the magnitude of the DC voltage exceeds a certain desirable voltage level; the certain desirable voltage level being lower than said undesirably high voltage level;   a lamp means having a pair of lamp input terminals operative to receive lamp current;   an inverter circuit having a pair of DC input terminals and a pair of AC output terminals; the DC input terminals being connected with the DC output terminals; and   lamp connection circuit operative to provide connection between the lamp input terminals and the AC output terminals, thereby to cause lamp current to be supplied to the lamp from the AC output terminals; the lamp connection circuit also having a control output connected with the control input and being operative to provide the control signal to the control input whenever the magnitude of the lamp current exceeds a certain desired current level, thereby to prevent the magnitude of the lamp current from exceeding the certain desired current level even though, in the absence of connection between the control output and the control input, the magnitude of the lamp current would have exceeded the certain desired current level.   
     
     
       2. The arrangement of claim 1 wherein the DC source includes a pre-conditioner circuit having an energy-storing inductor periodically charged from a primary DC voltage source and discharged into an energy-storing capacitor. 
     
     
       3. The arrangement of claim 1 wherein the lamp is a gas discharge lamp. 
     
     
       4. An arrangement comprising: an AC source operative to provide an AC source voltage at a pair of AC source terminals;   a conditioning circuit connected with the AC source terminals and operative to provide a DC supply voltage at a pair of DC output terminals; the conditioning circuit including a control circuit having an auxiliary control input receptive of an auxiliary control signal; the control circuit being operative: (a) when not being provided with said auxiliary control signal, to control the magnitude of the DC supply voltage so as to maintain it at or near a certain maximum desirable level substantially irrespective of significant changes in the magnitude of (i) any current flowing from the DC output terminals, and (ii) the AC source voltage; and (b) when being provided with said auxiliary control signal, to cause the magnitude of the DC supply voltage to be controlled to a level lower than said certain maximum desirable level; and   a ballast circuit having a pair of DC input terminals connected with the DC output terminals and being operative to provide an AC output from a set of AC output terminals; the AC output terminals being adapted to connect with and, when indeed so connected, to provide lamp current to a gas discharge lamp; the ballast circuit having a control output operative to provide a signal in response to the presence in the ballast circuit of a voltage or current of magnitude even slightly larger than a certain desirable magnitude; the control output being connected with the auxiliary control input, thereby (i) to provide said auxiliary control signal to the auxiliary control input, and (ii) to prevent the presence of such a voltage or current of magnitude substantially larger than said certain desirable magnitude.   
     
     
       5. The arrangement of claim 4 wherein, in case the magnitude of the DC supply voltage were to be at or near said certain maximum desirable level, the magnitude of the lamp current would be larger than said certain desirable magnitude. 
     
     
       6. The arrangement of claim 4 wherein, in case the control output were to become disconnected from the control input, the magnitude of the lamp current would be larger than said certain desirable magnitude. 
     
     
       7. The arrangement of claim 4 wherein the conditioning circuit is further characterized by including an intermittently conducting transistor and an energy-storing capacitor. 
     
     
       8. An arrangement comprising: an AC source operative to provide an AC source voltage at a pair of AC source terminals;   a conditioning circuit connected with the AC source terminals and operative to provide a DC supply voltage at a pair of DC output terminals; the conditioning circuit being characterized by: (i) including a pre-converter circuit having an intermittently charged energy-storing inductor and a control input, and (ii) causing the magnitude of the DC supply voltage to be regulated to a certain maximum level except when receiving a control signal at the control input; and   a ballast circuit having a pair of DC input terminals connected with the DC output terminals and being operative to provide an AC output voltage from a set of AC output terminals; the AC output terminals being adapted to connect with and, when indeed so connected, to provide lamp current to a gas discharge lamp; the ballast circuit having a control output operative, in response to the flow of lamp current, to provide a signal in the event the magnitude of the lamp current were to exceed a desired level by even a small amount; the control output being connected with the control input, thereby (i) to provide the control signal to the control input whenever the magnitude of the lamp current exceeds the desired level by such a small amount, and (ii) to prevent the magnitude of the lamp current from exceeding the desired level by anything more than such a small amount.   
     
     
       9. The arrangement of claim 8 wherein, in case the connection between the control output and the control input were to be broken, the magnitude of the lamp current would exceed the desired level by more than such a small amount. 
     
     
       10. The arrangement of claim 8 wherein, whenever the gas discharge lamp is not connected with the AC output terminals, the magnitude of the DC supply voltage is regulated to remain at or near said certain maximum level substantially regardless of changes in the magnitude of the AC source voltage. 
     
     
       11. The arrangement of claim 8 wherein the provision of the control signal serves to cause the magnitude of the DC supply voltage to decrease to a level below said certain maximum level. 
     
     
       12. An arrangement comprising: an AC source operative to provide an AC source voltage at a pair of AC source terminals;   a conditioning circuit connected with the AC source terminals and operative to provide a DC supply voltage at a pair of DC output terminals; the conditioning circuit being characterized by: (i) including a pre-converter circuit having an intermittently charged energy-storing inductor and a control input; and (ii) substantially regardless of changes in the magnitude of the AC source voltage, causing the magnitude of the DC supply voltage to be regulated to a certain level except when receiving a control signal at the control input; and   a ballast circuit having a pair of DC input terminals connected with the DC output terminals and being operative to provide an AC output voltage from a set of AC output terminals; the AC output terminals being adapted to connect with and, when indeed so connected, to provide lamp current to a gas discharge lamp; the ballast circuit having a control output operative, in response to the flow of lamp current, to provide a signal representative of the magnitude of the lamp current; the control output being connected with the control input, thereby to provide the control signal to the control input such as to cause the the magnitude of the DC supply voltage to be adjusted in such manner as to regulate the magnitude of the lamp current to a pre-determined level;   whereby: (a) when the lamp is not connected with the AC output terminals, the magnitude of the DC supply voltage is regulated to said certain level; and (b) when the lamp is connected with the AC output terminals, the magnitude of the lamp current is regulated to the pre-determined level by way of adjusting the magnitude of the DC supply voltage away from said certain level.   
     
     
       13. The arrangement of claim 12 wherein the AC source is an ordinary electric utility power line. 
     
     
       14. The arrangement of claim 12 wherein the lamp current is of a fundamental frequency substantially different from that of the AC source voltage. 
     
     
       15. An arrangement comprising: a source operative to provide an ordinary power line voltage at a pair of power line terminals; and   a frequency-converting ballast circuit connected with the power line terminals and characterized by: (i) including components the characteristics of which may fail to exactly meet certain specifications; (ii) having a pair of DC terminals across which is provided a DC voltage; (iii) having a pair of AC terminals adapted to connect with a gas discharge lamp, thereby to cause a lamp current to flow therethrough; (iv) causing the magnitude of the lamp current to be affected by any failure to exactly meet said certain specifications; (v) causing the magnitude of the lamp current to be proportional to the magnitude of the DC voltage; (vi) whenever the lamp is indeed connected with the AC terminals, causing the magnitude of the lamp current to be regulated to a desired current level substantially regardless of any failure to meet said certain specifications; and (vii) whenever the lamp is not connected with the AC terminals, causing the magnitude of the DC voltage to be regulated to a certain substantially constant level regardless of changes in the magnitude of the power line voltage;   whereby: (a) when the lamp is not connected with the AC terminals, the magnitude of the DC voltage is regulated to said certain substantially constant level substantially irrespective of changes in the magnitude of the power line voltage; and (b) when the lamp is in fact connected with the AC terminals, the magnitude of the lamp current is regulated to the pre-determined level by way of adjusting the magnitude of the DC voltage away from said certain substantially constant level, thereby to compensate for any failure to exactly meet said specifications.   
     
     
       16. An arrangement comprising: an AC source operative to provide an AC source voltage at a pair of AC source terminals;   a conditioning circuit connected with the AC source terminals and operative to provide a DC voltage at a pair of DC output terminals; the conditioning circuit being characterized by: (i) including a pre-converter circuit having an intermittently charged energy-storing inductor and a control input; and (ii) substantially regardless of changes in the magnitude of the AC source voltage, causing the magnitude of the DC voltage to be regulated to a certain level except when receiving a control signal at the control input; and   a ballast circuit having a pair of DC input terminals connected with the DC output terminals and being operative to provide an AC output voltage from a set of AC output terminals; the AC output terminals being adapted to connect with and, when indeed so connected, to provide lamp current to a gas discharge lamp; the ballast circuit having a control output operative, in response to the flow of lamp current, to provide a signal representative of the magnitude of the lamp current; the control output being connected with the control input, thereby to provide the control signal to the control input such as to cause the the magnitude of the DC voltage to be reduced in response to the flow of lamp current in excess of a pre-determined level;   such that: (a) when the lamp is not connected with the AC output terminals, the magnitude of the DC voltage is regulated to said certain level; and (b) when the lamp is connected with the AC output terminals, the magnitude of the DC voltage is regulated to a level lower than said certain level.   
     
     
       17. An arrangement comprising: an AC source operative to provide an AC source voltage at a pair of AC source terminals;   a conditioning circuit connected with the AC source terminals and operative to provide a DC voltage at a pair of DC output terminals; the conditioning circuit being characterized by, substantially regardless of changes in the magnitude of the AC source voltage, causing the magnitude of the DC voltage to be regulated to a certain level except when receiving a control signal at a control input; and   a ballast circuit having a pair of DC input terminals connected with the DC output terminals and being operative to provide an AC output voltage from a set of AC output terminals; the AC output terminals being adapted to connect with and, when indeed so connected, to provide lamp current to a gas discharge lamp; the ballast circuit having a control output operative, in response to the flow of lamp current, to provide a signal representative of the magnitude of the lamp current; the control output being connected with the control input, thereby to provide the control signal to the control input such as to cause the the magnitude of the DC voltage to be reduced in response to the flow of lamp current in excess of a pre-determined level;   such that: (a) when the lamp is not connected with the AC output terminals, the magnitude of the DC voltage is regulated to said certain level; and (b) when the lamp is connected with the AC output terminals, the magnitude of the DC voltage is regulated to a level lower than said certain level.   
     
     
       18. An arrangement comprising: an AC source operative to provide an AC source voltage at a pair of AC source terminals;   a conditioning circuit operable to be connected with the AC source terminals and functional, after indeed having been connected with the AC source terminals, to provide a DC supply voltage at a pair of DC output terminals; the conditioning circuit being characterized by (i) immediately after having been connected with the AC source terminals, causing the magnitude of the DC supply voltage to assume a certain relatively high level, and (ii) subsequently, in response to a control action received at a control input, to assume a relatively low level; the relatively high level being substantially higher than the relatively low level; and   a ballast circuit having a pair of DC input terminals connected with the DC output terminals and being operative to provide an AC output voltage from a set of AC output terminals; the AC output terminals being connected with a gas discharge lamp.   
     
     
       19. The arrangement of claim 18 wherein the ballast circuit has a control output connected with the control input; the control output being functional to provide said control action. 
     
     
       20. The arrangement of claim 19 wherein the control output provides said control action a short period after the conditioning circuit has been connected with the AC source terminals.